The effect of body orientation on a point-to-point movement in healthy elderly persons

Upper limb retraining during the early phases of neurological rehabilitation often involves having individuals practice reaching in body orientations that reduce the effect of gravity on various joint motions (e.g., shoulder flexion, elbow extension). However, the efficacy of these training techniques has not been determined. The purpose of this study was to determine the effects of reducing gravity through a change in body orientation from sitting to side-lying on the kinematics of a point-to-point movement in healthy elderly persons.

Nine healthy, right-hand-dominant women 62 to 66 years of age pointed to a target in two different body orientations-sitting and side-lying. A 2-dimensional kinematic analysis of the movement was performed to compare the trajectory of the hand and the interjoint coordination under the two conditions.

Regardless of body orientation relative to gravity, participants produced straight hand paths and smooth, bell-shaped velocity profiles. However, they moved slower in side-lying, and the pattern of interjoint coordination varied. The shoulder and elbow moved less, whereas the scapula made a greater contribution to the overall movement. Furthermore, the temporal coordination of the joints was modified as a consequence of body position.

The results indicate that point-to-point arm movements made against gravity differ from those made in a gravity-reduced plane, particularly at the joint level, illustrating that movement organization is sensitive to this contextual difference. The effect of minimizing gravity on upper limb movement needs to be explored in patient populations to determine whether training patients in gravity-reduced orientations is efficacious.